Studies on the chromosomes of genusNycticebus

The karyotypes of three species (N. coucang, N. intermedius, andN. pygmaeus) of genusNycticebus, collected from the southern Yunnan of China, have been studied. All individuals from three species possess 2n=50 chromosomes, and all chromosomes in their complement are biarm chromosomes. The karyotype of slow loris (N. coucang) is characterized by having a secondary constriction and Ag-NORs in the short arms of pair No. 1. The G-banding patterns of three species are very similar. Three species are found to have multiple Ag-NORs. InN. coucang, NORs were observed on five pairs (Nos. 1, 6, 9, 15, and 23) and inN. intermedius andN. pygmaeus, NORs were found on four pairs (Nos. 6, 9, 15, and 20). This finding indicates that slow lorises, as primitive primates, also have multiple NOR-bearing chromosomes. Finally, the classification of genusNycticebus by karyotype analysis is discussed, and our results suggest that there are at least two valid species, namely:N. coucang andN. pygmaeus.     

Genetic divergence in two featherback fishes, Chitala chitala and Notopterus notopterus

Allozyme and RAPD profiles reveal markers that discriminate Chitala chitala and Notopterus notopterus. Thirty‐five allozyme loci were scored from 23 allozyme systems. Species‐specific differences were found at 16 loci. Fifteen RAPD markers with 77 size fragments, 244–2902 bp, were identified. The number of fragments specific to C. chitala and N. notopterus was found to be 20 and 31, respectively. Theta estimates of 0.9798 (allozymes) and 0.9471 (RAPD) indicated a large genetic divergence between C. chitala and N. notopterus. The observed genetic heterogeneity clearly demonstrated that the two genera, Chitala and Notopterus, are distinct from each other.     

Polymorphic microsatellite markers isolated from partially enriched genomic library of Chitala chitala

A total eight polymorphic microsatellite loci were obtained from genomic library of Indian feather back, Chitala chitala (order Osteoglossiformes, family Notopteridae) and the 46 samples were analysed to determine genetic variation. The mean number of alleles per locus ranged from 4.50 to 5.25, and expected heterozygosity ranged from 0.124 to 0.852. Deviation from Hardy–Weinberg equilibrium expectations (P < 0.002) was observed at loci Cch2, Cch9 (Bhaghirathi) and Cch9 (Brahmaputra). The identified microsatellite loci were found promising for population genetics studies of C. chitala and related species Notopterus notopterus (family Notopteridae).     

DNA content in the genus Xenopus

Nuclear DNA amounts were determined by cytofluorometry for twelve species and subspecies of the genus Xenopus. Absolute values, in pg per nucleus, were obtained by direct comparison with human lymphocyte nuclei. The lowest DNA amount (3.55 pg) was found in X. tropicalis, which possess only 20 chromosomes, and the highest (16.25 pg), in the hexaploid X. ruwenzoriensis, with 108 chromosomes. The two recently discovered tetraploid species, X. sp.n. and X. vestitus have, respectively, 12.57 and 12.83 pg of DNA. Among the species and subspecies with 36 chromosomes, the DNA content ranges from 6.35 to 8.45 pg.     

Cytogenetics of the genus Parasarcophaga (Sarcophagidae: Diptera)

Somatic chromosome complements of five sympatric species of the genus Parasarcophaga, viz. P. misera, P. albiceps, P. argyrostoma, P. ruficornis and P. knabi, are described. All the species have five pairs of meta/submetacentric autosomes and an XX/XY sex chromosome pair which is highly variable in size and shape. In P. misera and P. albiceps they are tiny dots while in P. knabi the metacentric X and Y chromosomes constitute almost one third of the genome. In P. ruficornis and P. argyrostoma they are telocentric chromosomes of moderate size. A comparative study of the C-banding patterns of P. ruficornis, P. knabi, P. argyrostoma and P. misera shows that autosomes of the former three species possess characteristic C-bands in pericentric regions while in P. misera they are absent. The heterochromatic sex chromosomes are C-band positive in all the species. However, with the exception of the tiny sex chromosomes of P. misera, the X chromosomes of other species show shorter or longer regions which stain rather lightly. These C-banded areas correspond to the heterochromatic areas revealed in orcein stained preparations. The evolutionary implications of these results are discussed.     

Heterochromatic banding patterns in the chromosomes ofBrimeura (Liliaceae)

The two species of the genusBrimeura (Liliaceae),B. amethystina andB. fastigiata, show a strikingly disjunct geographical distribution. Both species have a bimodal chromosome complement, 2n = 28, which includes 10 large (L) and 18 small (S) chromosomes. Most of the L-chromosomes possess heterochromatic segments which show enhanced quinacrine fluorescence. The resulting banding patterns are species-specific. Two triploid plants have been found inB. fastigiata.     

Mitochondrial DNA variation in natural populations of endangered Indian Feather-Back Fish, Chitala chitala

Genetic variation at mitochondrial cytochrome b (cyt b) and D-loop region reveals the evidence of population sub-structuring in Indian populations of highly endangered primitive feather-back fish Chitala chitala. Samples collected through commercial catches from eight riverine populations from different geographical locations of India were analyzed for cyt b region (307 bp) and D-loop region (636–716 bp). The sequences of the both the mitochondrial regions revealed high haplotype diversity and low nucleotide diversity. The patterns of genetic diversity, haplotypes networks clearly indicated two distinct mitochondrial lineages and mismatch distribution strongly suggest a historical influence on the genetic structure of C. chitala populations. The baseline information on genetic variation and the evidence of population sub-structuring generated from this study would be useful for planning effective strategies for conservation and rehabilitation of this highly endangered species.     

NTRS, a new family of highly repetitive DNAs specific for the T1 chromosome of tobacco

Species-specific repeated DNAs are important for identifying genomic components of hybrid organisms in plant breeding and in taxonomic studies, and we have previously described the HRS60 and GRS families of highly repetitive DNA sequences in tobacco. Here we describe a new family of highly repetitive DNA sequences termed NTRS (SspI family) that we have isolated from Nicotiana tomentosiformis (Goodspeed) and characterized and that is specific for the genomes of several species of the subgenus Tabacum. In situ hybridization showed that NTRS sequences are present in three pairs of chromosomes of N. tomentosiformis, six pairs of chromosomes of N. kawakamii, and only one pair of chromosomes of N. tabacum at an intercalary site. The NTRS family is not present in the N. otophora genome. The majority of NTRS sequences appeared to be organized in tandem arrays in which local DNA structures sensitive to single strand-specific chemical probes, potassium permanganate, and osmium tetroxide complexed with pyridine revealed a periodicity of 220 bp, equal to the length of the repeat unit. The inner cytosine in CCGG and CC(A/T)GG sequences of the NTRS family is frequently methylated. Cloned and sequenced NTRS monomeric units are 212–219 bp in length and show 83.5%–95% mutual homology. They exhibit properties characteristic for molecules that possess stable intrinsic curvature, but there are differences among individual monomers in the degree of curvature. NTRS sequences like HRS60 and GRS sequences, were found to specify nucleosome positions. Received: 12 November 1996 / in revised form: 12 May 1997 / Accepted: 12 May 1997     

两种羽叶菊属植物(菊科:千里光族)的细胞学研究及其系统学意义

该研究首次报道了滇羽叶菊和台湾刘寄奴的染色体数据。结果表明:两者的染色体数量都为48,核型公式均为2n=2x=36m+10sm+2st,与前人报道的刻裂羽叶菊的核型稍有不同。两者的染色体形态均由大到小逐渐变化,核型二型性不明显,但前者染色体明显比后者大。这说明羽叶菊属染色体基数确实应为x=24,且染色体大小在种间有较大差异。细胞学证据表明,该属与蒲儿根属中染色体基数为x=24的类群以及狗舌草属确实近缘。     

Giemsa C-banding patterns in Aedes (Stegomyia) mosquitoes

Chromosomes from gonads of 14–24 h old pupae of nine species of Stegomyia mosquitoes have been examined using the Giemsa C-banding technique. The species studied were Aedes albopictus, A. polynesienis, A. scutellaris, A. alcasidi, A. seatoi, A. pseudalbopictus, A. melallicus, A. annandalei and A. vittatus. The diploid chromosome number of all species is six. All species possess C-bands in the centromeric regions of each of the three pairs of chromosomes. Besides, an intercalary C-band is present on the female determining (=m) chromosome but absent from the male—determining (= M) chromosome of all species except A. vittatus. In A. vittatus, the m and M chromosomes possess a terminal C-band. Thus, the nine species of Aedes analysed showed two distinct patterns of C-banding. —The evolution of heterochromatin patterns in various species is also discussed. The Giemsa C-banding technique should prove useful in studies of chromosomal speciation in culicine mosquitoes.     

HETEROCHROMATIN BANDING IN BOYKINIA,HEUCHERA, MITELLA,SULLIVANTIA, TIARELLA,AND TOLMIEA (SAXIFRAGACEAE)

Karyotypic differences were sought among species of Boykinia, Heuchera, Mitella, Sullivantia, Tiarella, and Tolmiea utilizing a modification of the Hy-banding technique. Prominent centromeric and some telomeric heterochromatin banding was observed. Boykinia aconitifolia and species of Sullivantia possess an identical banded karyotype, while four species of Heuchera, Mitella diphylla, Tiarella cordifolia, and Tolmiea menziesii (the latter at the tetraploid level) are characterized by a second, slightly different banded karyotype. In Sullivantia, Giemsa C-banding stains the same chromosomal regions revealed by Hy-banding. Larger amounts of heterochromatin are present in chromosomes of species of Heuchera, Mitella, Tiarella, and Tolmiea than in chromosomes of Sullivantia species and Boykinia aconitifolia. These karyological observations confirm generic relationships and demonstrate the systematic applicability of chromosome banding techniques to plants with very small chromosomes.     

A comparative cytogenetic study of five piranha species (Serrasalmus,Serrasalminae) from the Amazon basin

Cytogenetic studies were conducted on five piranha species belonging to the genus Serrasalmus, subfamily Serrasalminae (Serrasalmus altispinis, S. compressus, S. elongatus, S. manuelli, and S. spilopleura). All the species were collected in the Amazon basin: confluence of Negro and Solimõoes Rivers (CatalãoLake), Solimões River (Marchantaria Island – Camaleão Lake), Uatumã River (Hydroelectric Power Station of Balbina), and Pitinga River (Hydroelectric Power Station of Pitinga). All the five species possess 2n = 60 chromosomes with 5–12 subtelo- and acrocentric chromosomes bearing nucleolar organizer regions. A proximal C-band positive heterochromatin block was evident on the long arms of a medium-sized metacentric chromosome pair in all the analized species, thus making it a cytogenetic marker for the genus. It is hypothesized that 2n = 60 chromosomes represents a derived feature in terms of the chromosomal evolution of piranhas because the basal lineages possess 2n = 62. Both Robertsonian centric fusion and non-Robertsonian rearragements such as pericentric inversions seem implicated in the chromosomal evolution of this group.     

The karyotype of Nodipecten nodosus (Bivalvia: Pectinidae)

Earlier karyotypical work on Nodipecten nodosus embryos indicated that this species has a diploid number of 38, with six pairs respectively of metacentric and submetacentric chromosomes and seven pairs of subtelocentric chromosomes, although there were some difficulties in obtaining complete metaphases. The present work provides additional results on specific regions of the chromosomes in N. nodosus and, by meiotic studies, confirms the chromosome number with more reliability. Active nucleolar organizer regions (NOR), detected in mitotic metaphases from embryos, can be characterized in N. nodosus by a high level of heteromorphism of NOR-sites, indicating that these regions are not appropriate as chromosomal markers in this species. The procedure for detecting constitutive heterochromatin of chromosomes allowed us to observe most of the heterochromatic blocks at a pericentromeric position and some at telomeric and interstitial positions. The analysis of meiotic chromosomes from gonad tissue revealed the presence of 19 bivalents during metaphase I, all homomorphic and isopicnotic, confirming the previously described diploid chromosomal number of 38 for N. nodosus. From these results, some evolutionary aspects of the Pectinidae are briefly discussed.     

Genetic processes in intergeneric cell hybrids Atropa + Nicotiana

Summary The genetic constitution of the cell hybrids Atropa belladonna + Nicotiana chinensis, obtained by cloning of individual heteroplasmic protoplast fusion products (Gleba et al. 1982) and cultured in vitro for 12 months, has been studied. The study comprised 11 hybrid cell clones of independent origin and included analysis of a) chromosome number, size, morphology, and relative position in metaphase plates, b) multiple molecular forms of the enzymes esterase and amylase, and c) relative nuclear DNA content. The data obtained permit us to conclude that, after one year of unorganized growth in vitro, the cells of most (8) clones had retained chromosomes of both parents, while species-specific elimination of nearly all Atropa chromosomes had occurred in three clones. About half of the non-segregating clones possess 120–150 chromosomes including 50–70 of Atropa and 50–90 of Nicotiana. Other clones are polyploid and possess 200–250 chromosomes with a predominance of either Atropa or Nicotiana chromosome types. Only a few chromosomal changes (reconstituted chromosomes, ring chromosomes) have been detected. In some metaphase plates, chromosomes of the two parents tend to group separately, indicating non-random arrangement of chromosomes of the two parents within the hybrid nucleus. Cytophotometric studies of the relative nuclear DNA content showed that distribution histograms for cell clones were similar to those of non-hybrid cultured cells. Cell populations were relatively homogenous and do not indicate any genetic instability as a result of hybridization between remote plant species. Biochemical analysis of isoenzyme patterns confirmed that in most cell clones, species-specific multiple molecular forms of esterase and amylase from both parents were present, i.e. genetic material of both parental species was expressed in the cell hybrids.Dedicated to Professor G. Melchers with gratitude     

Nucleolar relationships in some Australian Chironomus species

Members of a group of Australian Chironomus species in the pseudothummi complex show wide variation in number and location of nucleolar organizing regions (NORs). The structure of these regions has been examined by phase contrast microscopy and silver banding of salivary gland polytene chromosomes. Presence of nucleoli was also checked on other types of chromosomes in some species. The contribution of the silver banding technique to nucleolar studies in these chironomid chromosomes is discussed. Nucleoli often seem to emerge from groups of (up to 9) bands. Further studies are necessary to confirm the presence of rRNA cistrons in all of these bands. Banding differences, in particular absence of bands from homologous regions of some species which have smaller nucleoli or lack particular nucleoli, have been found. In the case of Ch. tepperi, however, little banding difference is apparent in the 16B region between the N(IV)⁺ and N(IV)^– chromosomes, although in situ hybridization (Eigenbrod 1978) shows a deletion of rRNA cistrons in the N(IV)^– stock. Differences in heterochromatin amount have also been observed at different NORs. A scheme for the evolution of nucleolar-producing regions in this Chironomus group in terms of these and other known chromosomal changes is presented and discussed.     

CONSERVED SEX CHROMOSOMES ACROSS ADAPTIVELY RADIATED ANOLIS LIZARDS

Vertebrates possess diverse sex‐determining systems, which differ in evolutionary stability among particular groups. It has been suggested that poikilotherms possess more frequent turnovers of sex chromosomes than homoiotherms, whose effective thermoregulation can prevent the emergence of the sex reversals induced by environmental temperature. Squamate reptiles used to be regarded as a group with an extensive variability in sex determination; however, we document how the rather old radiation of lizards from the genus Anolis, known for exceptional ecomorphological variability, was connected with stability in sex chromosomes. We found that 18 tested species, representing most of the phylogenetic diversity of the genus, share the gene content of their X chromosomes. Furthermore, we discovered homologous sex chromosomes in species of two genera (Sceloporus and Petrosaurus) from the family Phrynosomatidae, serving here as an outgroup to Anolis. We can conclude that the origin of sex chromosomes within iguanas largely predates the Anolis radiation and that the sex chromosomes of iguanas remained conserved for a significant part of their evolutionary history. Next to therian mammals and birds, Anolis lizards therefore represent another adaptively radiated amniote clade with conserved sex chromosomes. We argue that the evolutionary stability of sex‐determining systems may reflect an advanced stage of differentiation of sex chromosomes rather than thermoregulation strategy.     

Karyotype studies in seven species of cyprinidae

The present report embodies karyotype studies of seven Indian cyprinids. Of these, the karyotypes of five species possess chromosomes all of which are acrocentric. These areLabeo calbasu (Ham.) 2n=54,Puntius sophore (Ham.),P. conchonius Ham.,P. stigma (Ham.) 2n=50 andChela bacaila (Ham.) 2n=52. The karyotype ofCrossocheilus latius punjabensis Mukerji has 48 chromosomes, 12 of which are metacentric (2n=12m+36r's). InAmblypharyngodon mola (Ham.), 52 chromosomes form the diploid set which include 8 metacentrics. In none of the seven species morphologically distinguishable sex chromosomes were found.Literature on cyprinid karyotypes has been reviewed in order to understand in how far the cytological characters are in agreement with the classification based on morphological studies. The validity ofMatthey's notion of nombre fondamental to establish kinship between cytologically known cyprinid species has also been discussed.     

Chromosome banding in amphibia

The distribution of constitutive heterochromatin on the chromosomes of Triturus a. alpestris, T. v. vulgaris and T. h. helveticus (Amphibia, Urodela) was investigated. Sex-specific chromosomes were determined in the karyotypes of T. a. alpestris (chromosomes 4) and T. v. vulgaris (chromosomes 5). The male animals have one heteromorphic chromosome pair, of which only one homologue displays heterochromatic telomeres in the long arms; the telomeres of the other homologue are euchromatic. This chromosome pair is always homomorphic and without telomeric heterochromatin in the female animals. There is a highly reduced crossing-over frequency between the heteromorphic chromosome arms in the male meiosis of T. a. alpestris; in T. v. vulgaris no crossing-over at all occurs between the heteromorphic chromosome arms. No heteromorphisms between the homologues exist on the corresponding lampbrush chromosomes of the female meiosis. In T. h. helveticus no sex-specific heteromorphism of the constitutive heterochromatin could be determined. The male animals of this species, however, already possess a chromosome pair with a greatly reduced frequency of chiasma-formation in the long arms. The C-band patterns and the pairing configurations of the sex-specific chromosomes in the male meiosis indicate an XX/XY-type of sex-determination for the three species. A revision of the literature about experimental interspecies hybridizations, gonadic structure of haploid and polyploid animals, and sex-linked genes yielded further evidence in favor of male heterogamety. The results moreover suggest that the heterochromatinization of the Y-chromosome was the primary step in the evolution of the sex chromosomes.     

An hypothesis and evidence concerning the genetic components controlling tumor formation in Nicotiana

Summary The evidence discussed in this paper demonstrates unuqual genetic contribution of N. debneyi-tabacum and N. longiflora to the development of tumors in hybrids between them. Tumor formation depends upon the presence of a specific longiflora chromosome fragment in an otherwise debneyi-tabacum background and consequently is transmitted as a dominant trait. Tumor expression remains relatively constant among those segregants which carry the complete complements of N. debneyi-tabacum or N. tabacum along with the longiflora chromosome, but tumors fail to develop on plants with a few debneyi chromosomes on a diploid longiflora background. These results suggest that gene(s) on a single longiflora chromosome fragment are sufficient, whereas from N. debneyi or N. tabacum a large number of genes distributed over many chromosomes are required for tumor formation. An hypothesis concerning genetic components controlling tumor initiation (I) and expression (ee) is proposed, supported by these observations, and by previous studies both genetic and physiological, on another tumorous hybrid between N. glauca and N. langsdorffii. (I) and (ee), representing unequal contributions from two evolutionarily diverse species, must both be present in the hybrid for tumors to develop. Evidence is presented to indicate that N. longiflora and N. langsdorffii, belonging to the section Alatae, represent species carrying (I) and that N. debneyi, N. tabacum and N. glauca, belonging to different sections of the genus Nicotiana, are (ee) carriers. It is predicted that genetic analyses will reveal that the genes for tumor initiation (I) will be carried invariably by species of the section Alatae, or the so-called plus group of Näf, and genes modifying expression (ee) by species from other sections but belonging to the so-called minus group. Specific characterization of (I) and (ee) in biochemical terms is under investigation.     

The fate of recombinant chromosomes and genome interaction in Nicotiana asymmetric somatic hybrids and their sexual progeny

Genomic in-situ hybridization (GISH) was used to monitor the behaviour of parental genomes, and the fate of intergenomic chromosome translocations, through meiosis of plants regenerated from asymmetric somatic hybrids between Nicotiana sylvestris and N. plumbaginifolia. Meiotic pairing in the regenerants was exclusively between chromosomes or chromosome segments derived from the same species. Translocation (recombinant) chromosomes contained chromosome segments from both parental species, and were detected at all stages of meiosis. They occasionally paired with respectively homologous segments of N. sylvestris or N. plumbaginifolia chromosomes. Within hybrid nuclei, the meiotic division of N. plumbaginifolia lagged behind that of N. sylvestris. However, normal and recombinant chromosomes were eventually incorporated into dyads and tetrads, and the regenerants were partially pollen fertile. Recombinant chromosomes were transmitted through either male or female gametes, and were detected by GISH in sexual progeny obtained on selfing or backcrossing the regenerants to N. sylvestris. A new recombinant chromosome in one plant of the first backcross generation provided evidence of further chromosome rearrangements occurring at, or following, meiosis in the original regenerants. This study demonstrates the stable incorporation of chromosome segments from one parental genome of an asymmetric somatic hybrid into another, via intergenomic translocation, and reveals their transmission to subsequent sexual progeny.